1. Field of the Invention
This invention relates generally to a corrosion-resistant protective coating. More specifically, this invention provides a corrosion-resistant protective coating for an apparatus and method of processing (e.g., etching, chemical or physical vapor deposition, etc.) a substrate in a chamber containing a plasma of a processing gas. In particular, this invention provides a corrosion-resistant protective coating or sealant which may be used to line or coat inside surfaces of a reactor chamber that are exposed to corrosive processing gas(es). The protective coating or sealant of the present invention prevents corrosion of the inside surfaces of a reactor chamber while a substrate is being processed in a plasma of a processing gas.
2. Description of the Prior Art
The semiconductor industry in the production of integrated circuit structures on semiconductor wafers relies on high through-put, single structure-processing reactors which can be used for a variety of different processes, such as thermal chemical vapor deposition (CVD), plasma-enhanced CVD (PECVD), plasma-assisted etching, and deposition topography modification by sputtering. The inside surface of the chamber walls of these substrate-processing reactors are subject to attack by chemicals within processing gases used in such processes.
Processing reactor chambers, which contain controlled gaseous environments at reduced pressures, are generally constructed of aluminum, although specialty alloys and materials such as quartz have been used at times. Due to the broad experience of the semiconductor industry with aluminum reaction chambers, an understanding of the effect of the presence of the aluminum upon products produced in the reactors has been developed. Thus, those working in the industry are comfortable with the use of aluminum reaction chambers.
However, more recently, the integrated circuit chip industry has recognized the need for yet higher standards of purity in the processing equipment used to fabricate the integrated circuit structures. It has, therefore, been proposed, by Ohini, in xe2x80x9cFluorine Passivation Technology of Metal Surfacexe2x80x9d, 8th Symposium on ULSI Ultraclean Technologyxe2x80x9d, The Proceedings, Jan. 26-28, 1989, to replace the anodized aluminum chambers with highly polished stainless steel pretreated in HF to remove oxides, passivated with a high purity F2 gas to form a non-stoichiometric iron fluoride, and then thermally treated to form an FeF2 coating. While the resulting film withstands gaseous halogen containing environments, it will corrode if exposed to an aqueous environment.
It has also been proposed by Ohmi, in xe2x80x9cOutgas-Free Corrosion-Resistant Surface Passivation of Stainless Steel for Advanced ULSI Process Equipmentxe2x80x9d, ECS Fall Meeting, Chicago, October, 1988 Symposium of Automated IC Manufacturing, to oxidize passivated highly polished stainless steel materials in O2 to form a protective oxide surface thereon. Such surfaces are said to be capable of withstanding visible attack by concentrated aqueous hydrochloric acid, i.e., without any visible evidence of evolution of gas, for as long as 30 to 40 minutes.
While a coating with a resistance to corrosion for 30-40 minutes would not normally be considered sufficient for industrial use, it must be pointed out that exposure to aqueous concentrated mineral acids such as hydrochloric acid is considered to be a worst case test, indicative of much longer resistance to corrosion by gaseous halogens.
Therefore, the use of such highly polished stainless steel materials would apparently satisfy the corrosion resistance requirements of the integrated circuit chip industry. However, the cost of the use of such materials in the construction of processing equipment, such as deposition and etching chambers, is prohibitive. For example, the substitution of an ordinary stainless steel material for aluminum in the construction of an etching or deposition chamber may result in a cost increase of about four times the cost of aluminum.
A ceramic barrier material has been placed on the inside surface of aluminum walls of processing reactor chambers to protect the aluminum walls from the corrosive attack of process halogen gases and plasma. U.S. Pat. No. 5,366,585 to Robertson et al., which is fully incorporated herein by reference thereto, teaches a ceramic barrier material comprising aluminum oxide (e.g. anodized aluminum substrates) for shielding the inner surface of walls of a process reactor chamber from chemical attack, while permitting the utilization of a relatively inexpensive metal to construct the chamber walls.
Lorimer et al. developed a method of forming a corrosion-resistant protective coating on an aluminum substrate, as described in U.S. Pat. No. 5,069,938. The protective coating is formed by first forming a high purity aluminum oxide layer on an aluminum substrate and then contacting the aluminum oxide layer with one or more high purity fluorine-containing gases at elevated temperature. The aluminum oxide layer may be either a thermally formed layer or an anodically formed layer having a thickness from at least about 0.1 micrometer up to about 20 micrometers. The preferred fluorine-containing gases will comprise acid vapors. Examples of fluorine-containing gases include gaseous HF, F2, NF3, CF4, CHF3, and C2F6. As is evidenced by the process and the description of the finished coating, the fluoride-containing gas penetrated the aluminum oxide (possibly to the aluminum surface beneath) to form fluorine-containing compounds within. The protective coating of Lorimer et al. is intended to protect the chamber walls of the processing apparatus from the chemicals used in chemical vapor deposition and etching processes. However, it has been determined that a thermal or anodized aluminum oxide coating of 20 micrometers or less on an aluminum surface does not prevent the gradual build up of fluoride-containing compounds such as aluminum trifluoride (AlF3), ammonium fluoride (NF4F), and aluminum oxyfluorides (AlOxFy) upon the outer surface of the coating. These compounds eventually peel off from the surface of the coating and become a source of particulate contamination.
Copending, commonly assigned U.S. patent application having Ser. No. 08/770,092, filed Dec. 19, 1996 and entitled xe2x80x9cBoron Carbide Parts and Coating in a Plasma Reactor,xe2x80x9d and incorporated herein by reference thereto, teaches the use of a B4C layer for protecting reactor chamber walls manufactured of aluminum alloy or aluminum alloy having a formed aluminum oxide layer. While the B4C layer makes an excellent bond with aluminum alloy or an aluminum oxide layer supported by an aluminum alloy, the surface of the B4C layer contains uniformly distributed fine pores (x5000) wherethrough electrolytes and reactive processing gases may pass and contact the aluminum alloy surface or the surface of the aluminum oxide layer being supported by an aluminum alloy, causing undercut corrosion. For example, if the reactive processing gas contains chlorine, during an etching process chlorine passes through the uniformly distributed fine pores of the B4C layer and contacts an aluminum-containing surface to react therewith to produce aluminum chloride. When the B4C layer is exposed to moisture or water, aluminum chloride reacts with water to produce aluminum hydroxide and hydrochloric acid which penetrates through the fine pores of the B4C layer to contact and react with the aluminum-containing surface to produce additional aluminum chloride, which reacts with water to produce additional aluminum hydroxide and additional hydrochloric acid. The produced aluminum hydroxide expands, creating stress on the B4C layer and delamination of the B4C layer appears.
Therefore, what is needed and what has been invented is a corrosion-resistant protective coating for a B4C layer supported by an aluminum material, where the corrosion-resistant protective coating is capable of resisting the corrosive attack of process halogen gases and plasma (as measured by accelerated corrosion resistance tests using concentrated aqueous acids). What is further needed and what has been invented is a high purity corrosion-resistant protective coating which may be utilized on the surface of a ceramic layer (e.g., B4C) supported by aluminum-containing parts used in vacuum process chambers so that aluminum may continue to be utilized in the construction of semiconductor wafer processing equipment for the integrated circuit chip industry without sacrificing purity standards.
In accordance with the present invention, a corrosion-resistant protective coating is provided to protect the inside surfaces of a reactor chamber containing corrosive processing gases which are used for processing (e.g., etching, chemical or physical vapor deposition, etc.) A substrate in the reactor chamber. The corrosion-resistant protective coating is preferably placed on a chamber wall of the reactor chamber. The protective coating of the present invention preferably comprises at least one polymer resulting from a monomeric anaerobic chemical mixture having been cured in the absence of oxygen. Preferably, the monomeric anaerobic chemical mixture comprises a major proportion of at least one methacrylate compound and a minor proportion of an activator compound (i.e., a polymerization catalyst) which initiates the curing process in the absence of oxygen or air. The monomeric anaerobic chemical mixture more particularly includes from about 30% by wt. to about 95% by wt. tetraethylene glycol dimethacrylate, from about 4% by wt. to about 50% by wt. 2-hydroxyethyl methacrylate, and from about 1% by wt. to about 5% by wt. Cumene hydroperoxide.
The present invention broadly provides a chamber assembly for processing substrates in a plasma (e.g. an inductively coupled RF plasma of a processing gas) comprising a processing chamber including a processing zone wherein substrates (i.e. semiconductor substrates) are processed. The processing chamber also includes the protective coating. Preferably, the protective coating is disposed on the chamber wall of the processing chamber. A pedestal assembly including a chuck assembly is disposed in the processing zone and has a receiving surface (more specifically, a puck member with a receiving surface) for receiving a substrate. The chamber assembly further comprises a processing power source, and a processing gas-introducing assembly engaged to the chamber wall for introducing a processing gas into the processing zone of the chamber wall. A processing power-transmitting member is connected to the processing power source for transmitting power into the processing zone to aid in sustaining a plasma from a processing gas within the processing zone of the processing chamber. The chamber assembly is part of a plasma reactor for processing substrates. A dielectric window, such as one having a generally dome-shaped configuration, is supported by the chamber wall. The processing power-transmitting member may be disposed in proximity to the dielectric window and may further be a coiled inductor or an antenna. The processing power source may be selected from the group consisting of an RF power source, a magnetron power source, and a microwave power source.
The present invention also broadly provides a method of processing (e.g., etching, chemical or physical vapor deposition, etc.) a layer (e.g., a metal layer, a dielectric layer, etc.) on a substrate comprising the steps of:
a) providing a substrate;
b) disposing the substrate in a reactor chamber containing a structure (e.g. a chamber wall) with a protective coating comprising a polymerized coating resulting from having cured a monomeric anaerobic chemical mixture (e.g., a mixture of tetraethylene glycol dimethacrylate, 2-hydroxyethyl methacrylate, and cumene hydroperoxide);
c) introducing a processing gas into the reactor chamber of step (b); and
d) introducing processing power into the reactor chamber of step (b) to process a layer on the substrate in a plasma of the processing gas.